December 7, 1989
1,500-M.P.H. Winds Found on Neptune
THE ASSOCIATED PRESS
AN FRANCISCO -- Neptune is swept by 1,500 mile-an-hour winds, the fastest yet discovered in the solar system, scientists have determined from analyzing photographs taken by Voyager 2.
The analysis also showed that the planet's moon Triton has at least four active ice volcanoes, two of which had been observed earlier. Because the spacecraft photographed only a portion of Triton, "chances are that there are a dozen of these things going off globally" at any time, said Torrence Johnson, a planetary scientist at the space agency's Jet Propulsion Laboratory in Pasadena, Calif. Johnson spoke at a news conference on Tuesday at the American Geophysical Union's fall meeting.
Neptune's jet-stream winds push frozen clouds of natural gas past the north edge of the planet's Earth-size, hurricane-like Great Dark Spot at nearly 1,500 miles per hour, the Voyager project scientist, Edward Stone, told reporters.
"These are the fastest we've observed," Stone said, adding that Neptune's winds easily exceed the previous record winds of 1,100 m.p.h. in Saturn's jet stream. Neptune gets only one nine-hundredth of the sunlight Earth receives.
Scientists Are Puzzled
Scientists are perplexed about how the internal heat left over from Neptune's formation is enough to drive 700-m.p.h. winds in the Great Dark Spot, not to mention the 1,500-m.p.h. jet stream winds blowing between 15 and 20 degrees south latitude, Stone said.
Part of the explanation may be that the flow of fluid gases in the planet's atmosphere may be so smooth that little energy is needed to power high winds, he said.
The clouds racing in Neptune's winds could be seen in a movie made by computer from still photographs taken by Voyager. Also shown at the news conference was another computer movie clearly showing two of the dark volcanic plumes on Triton, Neptune's largest moon and the coldest known object in the solar system.
Confirmation of the first active volcano was announced Oct. 2 after scientists analyzed photographs that Voyager 2 snapped during its Aug. 24-25 flight past Neptune and Triton. Detection of more such volcanoes, which spew nitrogen ice and gas 5 miles high and 90 miles downwind, was announced at the news conference.
Speculation About Venus
Triton is only the third world in the solar system known to have active volcanism. The others are Earth and Jupiter's moon Io, which has sulfur-spewing volcanoes. Scientists suspect there are volcanoes on cloud-shrouded Venus.
The volcanic plumes on Triton rise like columns, each forming a cloud that drifts back and forth as it is blown downwind. A shadow cast by one cloud also is visible.
The movie also shows what scientists suspect are two or three more plumes, Johnson said.
When Voyager swept past Triton early Aug. 25, scientists saw streaks on dark material deposited on the moon's surface by what they believed were active nitrogen-ice volcanoes.
A Movie About Computer
The National Aeronautics and Space Administration announced it was sure there was one active volcano after conducting stereoscopic analysis of the photos. But the images were so fuzzy "you had to take our word for it," Johnson said.
So NASA used a computer to overlap still photographs taken from different angles and replay them in sequence repeatedly. The resulting movie revealed additional volcanic plumes.
The causes of Neptune's high winds are mysterious.
Stone described one theory on the volcanoes: Darker material settles on the moon's surface, then is covered by transparent nitrogen ice. Sunlight penetrates the ice, and warms the darker material beneath. But the heat cannot escape through the ice, so some of the buried ice melts into gas, causing pressure to build until the gas erupts upward through cracks, carrying ice and dark material with it.
Voyager 2's Neptune-Triton exploration capped a 12-year mission in which it flew past Jupiter, Saturn and Uranus. The spacecraft discovered six moons at Neptune, bringing the total to eight, and found several rings of debris orbiting the planet, which is 30 times farther from the sun than Earth.